Removal of odor by hydrogenation and oxidation



United States Patent "ice 3,152,079 REMOVAL GE 0139?. BY ERG-GENATEGN AND OXEDATIQN Gerhard Lehmann, Hamburg-Hamburg, and Hellmuth Zahn, Hamburg-Neugrahen, Germany, assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 9, 1961, er. No. 151,176 Claims priority, application Germany, Apr. 27, 1951,

73,711 5 Claims. (Cl. 208-264) This invention relates to a new and improved process for treating various light petroleum streams to produce certain finished products which have relatively innocuous odor properties. The invention is particularly usefully applied to petroleum fractions boiling in the white spirit boiling range that have been desulfurized by hydrogenation.

It is known in the art that the disagreeable odor of certain untreated hydrocarbon mixtures, for instance crude mineral oil distillates, is largely due to their content of sulfur compounds. These sulfur compounds are likewise responsible for two other extremely undesirable properties of unpurified hydrocarbon mixtures, i.e., the corrosivity and pungent odor of their combustion products. Consequently, numerous processes have been proposed for reducing the sulfur content of such products while incidentally elfecting a slight odor improvement in the materials. The best known and most frequently employed process consists in treating the sulfur-containing products with concentrated sulfuric acid or oleum.

Several other processes have been proposed to reduce the sulfur content of various hydrocarbon mixtures. For instance, it is known to refine the oils in the liquid or vapor phase with aqueous solutions of oxidizing chemicals such as potassium permanganate or potassium dichromate. However, this method has not fund general acceptance due to the relatively large quantities of oxidants required and the difficulty of removal of the resultant by-products. Moreover, such treatment often results in undesirable discoloration of the treated hydrocarbon oils, and the odor of the oils obtained is usually not acceptable. A further shortcoming common to most oxidizing or metal-sweetening processes is that the odor stability of the resultant products during prolonged storage or when under the influence of light and/ or heat is adversely afiected. That is, it is believed certain disulfides are formed during the sweetening treatment and that these disulfides subsequently revert to corrosive, malodorous sulfur compounds during storage or while under the infiuence of heat and/ or light.

Recent years have seen an increasing desulfurization of light hydrocarbon products by means of catalytic hyrogenation. A particularly useful process of this type involves reacting the distillates to a greater or lesser extent in the presence of hydrogen and commonly a catalyst, in such a way that the sulfur compounds are reacted to form hydrogen sulfide. Such processes may broadly be called hydrogenation. Two processes of this type are called hydrofining and autofining. In autofining the distillate is treated at between 340 and 440 C. and 25 to 500 psi. in such a manner that the process is substantially self-supporting with respect to the amount of hydrogen needed in the presence of a dehydrogenation-hydrogenation catalyst which is immune to sulfur poisoning and combines activity for the dehydrogenation of naphthenes to aromatics with activity for the hydrogenation of organicah ly combined sulfur to hydrogen sulfide. A preferred catalyst comprises the combined oxides of cobalt and molybdenum supported on alumina. Hydrofining comprises a mild hydrogenation using a fixed bed of a suitable catli filfi l atented Oct. 6, 1964 alyst (such as cobalt molybdate or moybdenum on alumina or nickel-tungsten sulfide) that operates at temperatures in the range of 260-370 C., pressures from to 1000 p.s.i.g. with recycle hydrogen rates in the order of 200 to 100 standard cubic feet per barrel of oil charged. Particularly useful hydrofining conditions comprise pressure in the neighborhood of 200 p.s.i.g. at about 1 v./v./ hr. and around 3l6-343 C., using cobalt molybdate on alumina catalyst and consuming in the region of 1000 c.f./b. hydrogen.

It is possible to select hydrogenation conditions as described above in such a way that practically sulfur-free products are obtained having a sulfur content of less than 10 ppm. Despite such drastic desulfurization processes, which are scarcely obtainable with other conventional processes, the resultant products still have a slight, disagreeable odor, which is a drawback for the direct use of the said hydrocarbon mixtures as solvents, diluents or detergents, and particularly as extraction agents in the edible fats industry.

It is recognized in the art that in order to obtain application products which comply with the extremely high requirements as to odor, an additional step is required after the hydrocarbon mixture is subjected to the abovedescribed catalytic hydrogenation.

An example of such a 2-step process for the production of an odorless hydrocarbon mixture is hydrogenation followed by a sulfuric acid treatment. This process is extensively used in practice and in many cases results in satisfactory odorless and odor-stable products. However, certain hydrocarbon mixtures, for instance special gasolines obtained from Persian crude, cannot be successfully treated with this method, for they retain an unpleasant pungent odor. Moreover, this process has several considerable drawbacks, for example, the sulfuric acid treatment causes difiiculties with respect to (l) the corrosivity, (2) the removal of the by-products, (3) an increase in the boiling range of special and test gasolines, (4) extensive refining losses owing to the solubility of the hydrocarbons in concentrated sulfuric acid, and (5) fairly complex after-treatment with caustic soda washing with repeated water washings being required. It is also known to after-treat hydrogenated hydrocarbon products with caustic alkali solutions, for instance a caustic soda solution, in order to improve the odor, but the resultant products are not sufficiently odorless for the abovereferenced applications.

Heavy metals or heavy metal compounds, preferably oxides or salts have been proposed as the second process phase, after the catalytic hydrogenation treatment. Copper or iron oxides, for example, are recommended as active reagents with vaporous hydrocarbons, whereas sodium plumbite, lead acetate and copper ammonium acetate have been used in liquid phase treatments. A drawback of the vapor phase processes is that they have to be continuous and require very expensive equipment, so that they are hardly suitabble for smaller throughputs. On the other hand, in the liquid treatment process difficulties occur in the regeneration or removal of the heavy metalcontaining waste products. Undesirable discoloration of the resultant products and storage instability is frequently encountered.

Another process proposed for producing gasolines of the highest grade of purity with acceptable odor properties includes a combination of soda washings, hypochlorite treatment, hydrogenation and sulfuric acid refining. This process is considered technically and economically impracticable due to the extremely large amounts of chemicals required and work entailed; it does, however, clearly show the practical difliculties involved in the manufacture of odorless hydrocarbon mixtures.

It is an object of the present invention to produce light storage and under the influence of light and/ or heat can be obtained by catalytic hydrogenation of crude products with subsequent treatment of the hydrogenated product with aqueous solutions of oxidizing salts of alkali and alkaline earth metal acids having ahigh oxygen content,

i.e., containing anions such as permangantes, chromates,

and dichromates.

The advantages of this process are particularly striking when compared with the processes described above. For example, the quality of the products obtained by means of the instant invention is superior and the said aqueous salt solutions are considerably easier to store than concentrated sulfuric acid, for example. Moreover, there are no corrosion problems, while only small refining losses occur without any change whatever in the boiling ranges of the treated products, and the only after-treatment required with the instant invention is an intensive waterwashing.

Potassium permanganate has been found to be a particularly suitable oxidant for the second process step of the invention. This substance has the additional advan- 3O tage that the problem of waste product removal can be technically solved in a very favorable manner. The spent pyrolusite-containing neutral or weakly alkaline waste water according to the invention can be readily subjected to the usual waste water purification, i.e., flocculation of 5 the oleaginous waste Water with hydroxide slurries, settlement and subsequent filtration.

The catalytic hydrogenation step may be carried out according to 'the conventional methods described above.

The conditions of hydrogenation are preferably selected 40 so as to obtain the most drastic possible desulfurization. The aqueous solutions of oxidizing salts used in the second step of the process should not be too highly concentrated as the oxidative attack on the hydrocarbon mixture would otherwise be too intense and again lead to odor deterioration. The optimum concentration of the salt solution depends on the nature of the hydrocarbons to be treated; it generally varies from 0.5 to 6% by weight, preferably from 1 to 3% by weight. Neutral aqueous solutions of the said salts or of salts with an additional content of free alkali, such as sodium hydroxide, of up to approximately 3% by weight, have been found particularly suitable. Acidified solutions are slightly inferior with respect to odor improvement.

The quantity of salt solutions required for treatment of the hydrogenated hydrocarbon is generally in the range suitable for refining with liquid refining agents, i.e., from 0.5 to about 3% by volume, based on the quantity of hydrocarbon mixture to be treated, and preferably about 1% by volume. It has been found that smaller amounts of relatively higher concentrated solutions are more advan tageous than correspondingly larger amounts of weaker solutions; for instance, 1% by volume of 3% potassium permanganate solution yielded a product having a better, i.e., weaker, odor than 3% by volume of a 1% solution. On the Whole, therefore, surprisingly small quantities of the salt solution are used in the second step of the instant process.

Normal room or ambient tempereature has been found to be the most suitable treating temperature for the second step of the instant process. Seasonal fluctuations of from about 10 to 30 C. have practically no effect, whereas considerably elevated temperatures of, for instance, C. result in less favorable products, particularly with respect to reduced odor improvement and deterioration of odor properties on storage.

The second step of the process of the invention may be carried out batchwise or continuously. The duration of either type of treatment depends on the specific operating conditions required. In the treatment of separate batches in stirred containers, it is obvious that the entire contents of the container should be thoroughly mixed, approximately 1-3 hours being required, depending on the power and dimensions of the stirrer. In a preferred embodiment of the invention, the hydrogenated hydrocarbons are treat ed with an aqueous solution of the oxidizing salts of metal acids having a high oxygen content in a rotating disc contactor as described in US. Patent 2,601,674 to Reman, issued June 24, 1952. Excessively long processing periods should be avoided as they again result in odor deterioration. After settlement and separation of the spent salt solutions, the treated hydrocarbon mixture should be thoroughly rewashed.

EXAMPLE I The advantages of the process of the instant invention over those of other 2-phase treatment methods are elucidated in the following table. The first process step is the Table I Refining Process:

Step (1) Catalytic hydrogenation Step (2) Caustic soda Plumbite Hypochlorite Permanganate Chromate Hydrogen washings sweetening treatment treatment treatment peroxide Ozone treatment treatment REFINING AGENTS or THE SECOND srnr F0rmula Pb(NaOz) NaClO KMDO4 K2Cl'207 H202 ()3.

Concentration in 1.5 g. PbO 10 g. 3-35 g./l. active 3% w 3% w 3% w.

aqueous solution N aOH per chlorine 1.2% compound. ml. water. w. N aOH.

Quantity 2 x 10% by 10% by volume 0.5% by volume..-" 1% by volume- 1% by vol- 1% by vol- Up to -5 times the volume. ume. ume. theoretical oxygen requirement.

Contact time, in m 10 10 1O 10 2.

minutes.

Final odor of the No improve- Unexceptional Partly good, when Innocuous Good 8 N 0 improve- No improvement; a

treated test ment. the experiment ment. peroxide odor material. Was continued. when the experi- Odor of chlorine ment is continued. compounds was noted.

The ozone required was prepared from dry oxygen with the aid of an ozonizer and introduced into the hydrocarbon mixture with a hit. b The theoretical oxygen requirement; of the hydrocarbon mixture was calculated from the KMI104 consumption during titration. a Treatment at elevated temperatures essential (approximately 10 below boiling point results in discoloration with products having a boiling point Storage, heat and light did not adversely afiect the odor properties.

same in all examples and consists of a catalytic hydrogenation effected in such a way that the hydrogenated products had a sulfur content of approximately 0.0005% (5 p.p.m.). (Reaction conditions were: temperature, about 330 C.; pressure, about 34 atm.; molar ratio of hydrogenoil, about 1:7; space velocity, about 4 liters of liquid starting material per cu. dm. of catalyst per hour.) For the second process step, comparative experiments were carried out. Unless otherwise stated, the treatment was effected at room tempereature. The treatment after the second step invariably consisted of intensive washings. The several treating methods were tested on several special gasolines and one test gasoline having boiling ranges of from 150-190 C. All materials responded in practically the same way to the separate treating agents so that th results of the comparative experiments listed in the table are generally characteristic of the entire range of light hydrocarbon mixtures.

The results set forth in Table I above show that an unexpected improvement in the odor of hydrocarbon mixtures can be obtained by combining catalytic hydrogenation with a subsequent treatment with chromates or permanganates. It is further evident that similar results cannot be obtained with conventional 2-step processes such as hydrogenating with subsequent caustic soda washing or plumbite treatment unless certain undesirable phenomena such as discoloration are tolerated. Nor were products having improved odor characteristics obtained when permanganate, chromate, or dichromate were replaced by other, strong oxidants.

EXAMPLE H A further example of the process according to the invention is as follows: A mineral oil fraction having a boiling range of from about C. to about 200 C. was desulfurized by a catalytic oxygen treatment until the residual sulfur content was from about 2 to 7 p.p.m., with the following reaction conditions being observed: temperature, 330 C. to 360 C.; pressure, 30 to atm. gauge; molar ratio of hydrogen/ oil, 1.5-2.0; space velocity, 3 to 5 liters of liquid starting material per cu. dm. of catalyst per hour. The product was then decomposed into a broad lighter fraction, and three to four higher boiling fractions having narrower boiling ranges. These fractions were separately treated in stirred containers at normal temperatures with 1% by volume of neutral potassium permangate solution. For the lighter fraction :1 1.5-2% solution was sufiicient, a 3% potassium permanganate solution being used for the heavier fractions. After stirring for one hour the spent pyrolusite-containing solution was allowed to settle and separated. The gasolines were then Water-washed with vigorous stirring, the lighter fraction being washed twice and the heavier fractions three times. The latter then represented the finished special or test gasolines. The lighter fraction was decomposed by repeated redistillation into current products having narrower boiling ranges.

The finished products obtained had a barely preceptible, mild odor which was unchanged after months of storage in tanks or even in daylight. No appreciable deterioration of the odor occured even when the products were heated at approximately C. for 48 hours.

We claim as our invention:

1. A process for the production of odorless or weakly odorous hydrocarbon mixtures from odoriferous hydrocarbon mixtures comprising catalytic hydrogenation of the odoriferous hydrocarbon mixtures and subsequent treatment of the hydrogenated material in the liquid phase with an aqueous solution of salts of metal acids having a high oxygen content wherein the metal is selected from the group consisting of alkali and alkaline earth metal and the anion is selected from the group consisting of permanganates, chromates and dichrornates.

2. A process according to claim 1 wherein the aqueous solution is potassium permanganate.

3. A process according to claim 1 wherein the aqueous solution has a salt content from about 0.5 to about 5% by weight.

4. A process according to claim 1 wherein the aqueous solution contains minor quantities of free alkali.

5. A process according to claim 1 wherein about 1% by volume of the aqueous solution based on the hydrocarbon mixture is used.

References Cited in the file of this patent UNITED STATES PATENTS 2,034,197 Morrell Mar. 17, 1936 2,755,227 Lucas July 17, 1956 2,843,528 Jacobs et a1 July 15, 1958 2,897,142 Jacobs et al. July 28, 1959 

1. A PROCESS FOR THE PRODUCTIN OF ODORLESS OR WEAKLY ODOROUS HYDROCARBON MIXTURES FROM ODORIFEROUS HYDROCARBON MIXTURES COMPRISING CATALYTIC HYDROGENTATION OF THE ODORIFEROUS HYDROCARBON MIXTURES AND SUBSEQUENT TREATMENT OF THE HYDROGENATED MATERIAL IN THE LIQUID PHASE WITH AN AQUEOUS SOLUTION OF SALTS OF METAL ACIDS HAVING A HIGH OXYGEN CONTENT WHEREIN THE METAL IS SELECTED FROM THE GROUP CONSISTING OF ALKALI AND ALKALINE EARTH METAL AND THE ANION IS SELECTED FROM THE GROUP CONSISTING OF PERMANGANATES, CHROMATES AND DICHROMATES, 